gdb: add pyproject.toml

When running black to format Python files, files with extension .py.in
are ignored, because they don't end in .py.  Add a pyproject.toml file
to instruct black to pick up these files too.

gdb/ChangeLog:

	* py-project.toml: New.
	* gdb-gdb.py.in: Re-format.

gdb/testsuite/ChangeLog:

	* gdb.python/py-framefilter-gdb.py.in: Re-format.
	* gdb.python/py-framefilter-invalidarg-gdb.py.in: Re-format.

Change-Id: I9b88faec3360ea24788f44c8b89fe0b2a5f4eb97